I also don't like the idea of leaving a firearm unattended in a vehicle. Of course I used to live in a very densely populated area of Dallas. Smack in the middle of the junction of decent, really nice and downright crappy neighborhoods. Major street with lots of random foot traffic.
Where I live now, I get the feeling that the practice is far more commonplace, but I still don't do it.
Usually it's just what I'm carrying, though sometimes on trips I'll throw my 642 in the console. It's easier to get to than my G19 IWB under my shirt and seatbelt.
If I were going to have a dedicated truck (SUV actually) gun, theoretically I would lean towards a big bore revolver. In a pinch, my 3.5" Cimarron Thunderer in .45 Colt might work. I'm just spitballing here, but if there existed say a 3" 5 shot Smith in the flavor of .44 Special... Again, just dreamin'.
All that being said, having to light off anything mentioned in the cab of a vehicle would be less than pleasant, however effective. Maybe you are on to something.
Cool gun, BTW.
Edited to add: This is assuming handguns, as I live in town. If I were going to be in or lived in a more rural area, either of my lever rifles (.45 Colt or .30-30) or MAYBE my AR.